The present invention relates generally to the field of electrosurgery and, more particularly, to surgical devices and methods that employ high frequency energy to cut and ablate tissue for increasing the flow of blood to a region around the target tissue.
Coronary artery disease, the build up of atherosclerotic plaque on the inner walls of the coronary arteries, causes the narrowing or complete closure of these arteries resulting in insufficient blood flow to the heart. A number of approaches have been developed for treating coronary artery disease. In less severe cases, it is often sufficient to treat the symptoms with pharmaceuticals and lifestyle modification to lessen the underlying causes of the disease. In more severe cases a coronary artery blockage can often be treated using endovascular techniques, such as balloon angioplasty, a laser recanalization, placement of stents, and the like.
In cases where pharmaceutical treatment and endovascular approaches have failed or are likely to fail, it is often necessary to perform a coronary artery bypass graft procedure using open or thoracoscopic surgical methods. For example, many patients still require bypass surgery due to such conditions as the presence of extremely diffuse stenotic lesions, the presence of total occlusions and the presence of stenotic lesions in extremely tortuous vessels. However, some patients are too sick to successfully undergo bypass surgery. For other patients, previous endovascular and/or bypass surgery attempts have failed to provide adequate revascularization of the heart muscle.
The present invention is particularly concerned with an alternative to the above procedures, which is known as laser myocardial revascularization (LMR). LMR is a recent procedure developed with the recognition that myocardial circulation occurs through arterioluminal channels and myocardial sinusoids in the heart wall, as well as through the coronary arteries. In LMR procedures, artificial channels are formed in the myocardium with laser energy to provide blood flow to ischemic heart muscles by utilizing the heart""s ability to perfuse itself from these artificial channels through the arterioluminal channels and myocardial sinusoids. In one such procedure, a CO2 laser is utilized to vaporize tissue and produce channels in the heart wall from the epicardium through the endocardium to promote direct communication between blood within the ventricular cavity and that of existing myocardial vasculature. The laser energy is typically transmitted from the laser to the epicardium by an articulated arm device. Recently, a percutaneous method of LMR has been developed in which an elongated flexible lasing apparatus is attached to a catheter and guided endoluminally into the patient""s heart. The inner wall of the heart is irradiated with laser energy to form a channel from the endocardium into the myocardium for a desired distance.
While recent techniques in LMR have been promising, they also suffer from a number of drawbacks inherent with laser technology. One such drawback is that the laser energy must be sufficiently concentrated to form channels through the heart tissue, which reduces the diameter of the channels formed by LMR. In addition, free beam lasers generally must completely form each artificial lumen or revascularizing channel during the still or quiescent period of the heart beat. Otherwise, the laser beam will damage surrounding portions of the heart as the heart beats and thus moves relative to the laser beam. Consequently, the surgeon must typically form the channel in less than about 0.08 seconds, which requires a relatively large amount of energy. This further reduces the size of the channels that may be formed with a given amount of laser energy. Applicant has found that the diameter or minimum lateral dimension of these artificial channels may have an effect on their ability to remain open. Thus, the relatively small diameter channels formed by existing LMR procedures (typically on the order of about 1 mm or less) may begin to close after a brief period of time, which reduces the blood flow to the heart tissue.
Another drawback with current LMR techniques is that it is difficult to precisely control the location and depth of the channels formed by lasers. For example, the speed in which the revascularizing channels are formed often makes it difficult to determine when a given channel has pierced the opposite side of the heart wall. In addition, the distance in which the laser beam extends into the heart is difficult to control, which can lead to laser irradiation with heating or vaporization of blood or heart tissue within the ventricular cavity. For example, when using the LMR technique in a pericardial approach (i.e., from outside surface of the heart to inside surface), the laser beam may not only pierce through the entire wall of the heart but may also irradiate blood within the heart cavity. As a result, one or more blood thromboses or clots may be formed which can lead to vascular blockages elsewhere in the circulatory system. Alternatively, when using the LMR technique in an endocardial approach (i.e., from the inside surface of the heart toward the outside surface), the laser beam may not only pierce the entire wall of the heart but may also irradiate and damage tissue surrounding the outer boundary of the heart.
Revascularization, or the promotion of blood flow to tissue, is desirable in areas of the body other than the heart. For example, the meniscus tissue, a C-shaped piece of fibrocartilage located at the peripheral aspect of the joint, typically has very little blood supply (particularly the inner portions of the meniscus). For that reason, when damaged, the meniscus is unable to undergo the normal healing process that occurs in most of the rest of the body. In addition, with age, the meniscus begins to deteriorate, often developing degenerative tears. Typically, when the meniscus is damaged, the torn pieces begins to move in an abnormal fashion inside the joint. Because the space between the bones of the joint is very small, as the abnormally mobile piece of meniscal tissue (meniscal fragment) moves, it may become caught between the bones of the joint (femur and tibia). When this happens, the knee becomes painful, swollen and difficult to move. Thus, it would be desirable to revascularize portions of the meniscus, particularly after it has been torn or otherwise damaged to facilitate the healing process.
The present invention provides systems, apparatus and methods for selectively applying electrical energy to structures within or on the surface of a patient""s body. The present invention allows the surgical team to perform electrosurgical interventions, such as ablation and cutting of body structures, while limiting the depth of necrosis and limiting damage to tissue adjacent the treatment site. The systems, apparatus and methods of the present invention are particularly useful for canalizing or boring channels, divots, trenches or holes through tissue to revascularize the region around this tissue.
In a method according to the present invention, an electrode terminal is positioned in close proximity to a target site and a high frequency voltage difference is applied between the electrode terminal and a return electrode to volumetrically remove or ablate tissue at the target site. The electrode terminal(s) may be translated relative to the body structure during or after the application of electrical energy to sculpt a void within the body structure, such as a hole, channel, stripe, crater, divot or the like. In some embodiments, the electrode terminal(s) are axially translated toward the body structure to volumetrically remove one or more channel(s), divot(s) or hole(s) through a portion of the structure. In other embodiments, the electrode terminal(s) are translated across the body structure to remove one or more stripe(s) or channel(s) of tissue. In most embodiments, electrically conducting fluid, such as isotonic saline, is located between the electrode terminal(s) and the body structure. In the bipolar modality, the conducting fluid generates a current flow path between the electrode terminal(s) and one or more return electrode(s). High frequency voltage is then applied between the electrode terminal(s) and the return electrode(s) through the current flow path created by the electrically conducting fluid.
In one aspect of the invention, a method is provided for revascularization of the meniscus, particularly the inner aspect of the meniscus. The present invention may be useful for revascularization of a healthy meniscus, or a torn or damaged meniscus during a repair procedure. In the latter case, the torn pieces of the meniscus are typically removed, and one or more implants are anchored into the meniscus to fixate the tissue during healing. In one embodiment of the present invention, artificial channels or lumens are created during this procedure to help revascularize the damaged meniscus and facilitate the healing process. For example, in a xe2x80x9cbucket-handlexe2x80x9d lesion, the meniscus typically has a longitudinal tear or lesion. According to the present invention, one or more electrode terminals are positioned adjacent the inner aspect of the meniscus, and a high frequency voltage is applied between the electrode terminal(s) and one or more return electrode(s). The high frequency voltage ablates, i.e. volumetrically removes the tissue, and the electrode terminal(s) are axially translated into the space vacated by the removed tissue to bore a channel through the tissue. The channels are formed across the lesion from the inner aspect to the outer aspect of the meniscus to promote direct communication between blood within the outer aspect and that of existing meniscus vasculature to increase blood flow therein. In an exemplary embodiment, surgical implants are then advanced through the holes created by the present invention to fix the meniscus during healing.
In a specific configuration, the meniscus tissue is removed by molecular dissociation or disintegration processes. In these embodiments, the high frequency voltage applied to the electrode terminal(s) is sufficient to vaporize an electrically conductive fluid (e.g., gel or saline) between the electrode terminal(s) and the tissue. Within the vaporized fluid, a ionized plasma is formed and charged particles (e.g., electrons) are accelerated towards the tissue to cause the molecular breakdown or disintegration of several cell layers of the tissue. This molecular dissociation is accompanied by the volumetric removal of the tissue. The short range of the accelerated charged particles within the plasma layer confines the molecular dissociation process to the surface layer to minimize damage and necrosis to the underlying tissue. This process can be precisely controlled to effect the volumetric removal of tissue as thin as 10 to 150 microns with minimal heating of, or damage to, surrounding or underlying tissue structures. A more complete description of this phenomena is described in commonly assigned U.S. Pat. No. 5,683,366.
One of the advantages of the present invention, particularly over previous methods involving lasers, is that the surgeon can more precisely control the location, depth and diameter of the revascularizing channels formed in the tissue. The ability to precisely control the volumetric removal of tissue results in a field of tissue ablation or removal that is very defined, consistent and predictable. This precise heating also helps to minimize or completely eliminate damage to healthy tissue structures, cartilage, bone and/or cranial nerves that are often adjacent the target tissue. In addition, small blood vessels at the target site are simultaneously cauterized and sealed as the tissue is removed to continuously maintain hemostasis during the procedure. This increases the surgeon""s field of view, and shortens the length of the procedure. Moreover, the electrode terminal remains in contact with the meniscus tissue as the high frequency voltage ablates this tissue (or at least substantially close to the tissue, e.g., usually on the order of about 0.1 to 2.0 mm and preferably about 0.1 to 1.0 mm). This preserves tactile sense and allows the surgeon to more accurately determine when to terminate cutting of a given channel so as to minimize damage to surrounding tissues and/or minimize bleeding into the knee cavity.
Apparatus according to the present invention generally include an electrosurgical probe or catheter having a shaft with proximal and distal ends, one or more electrode terminal(s) at the distal end and one or more connectors coupling the electrode terminal(s) to a source of high frequency electrical energy. For revascularization of meniscus tissue, the distal end portion of the shaft will usually have a diameter of less than 3 mm, preferably less than 1 mm, to facilitate the formation of small hole(s) or channel(s) through the tissue. The electrode terminal(s) are preferably supported within an electrically insulating support member typically formed of an inorganic material, such as ceramic or glass. The electrode terminal(s) may extend outward from the support member by a distance of about 0.0 mm to about 10 mm, usually about 0.2 to about 5 mm. In an exemplary embodiment, the instrument comprises an array of electrically isolated electrode terminal(s) and one or more power limiting elements for limiting the application of power to the electrode terminal(s) in an electrically conducting fluid environment.
In open procedures, or in procedures in xe2x80x9cdryxe2x80x9d fields, the apparatus may further include a fluid delivery element for delivering electrically conducting fluid to the electrode terminal(s) and the target site. The fluid delivery element may be located on the probe, e.g., a fluid lumen or tube, or it may be part of a separate instrument. In arthroscopic procedures, however, the knee cavity will typically be filled with electrically conducting fluid (e.g., isotonic saline) so that the apparatus need not have a fluid delivery element. In both embodiments, the electrically conducting fluid will preferably generate a current flow path between the electrode terminal(s) and one or more return electrode(s). In an exemplary embodiment, the return electrode is located on the probe and spaced a sufficient distance from the electrode terminal(s) to substantially avoid or minimize current shorting therebetween and to shield the return electrode from tissue at the target site.